Location: Northwest Watershed Management Research
Title: Measurement of surface energy fluxes in a rangeland ecosystem and comparison with a multi-layer canopy model Authors
Submitted to: Journal of Hydrometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 2012
Publication Date: June 30, 2012
Citation: Flerchinger, G.N., M.L. Reba, and D. Marks. 2012. Measurement of surface energy fluxes from two rangeland sites and comparison with a multilayer canopy model. Journal of Hydrometeorology 13(3):1038-1051, doi: 10.1175/JHM-D-11-093.1. Interpretive Summary: Understanding the role of ecosystems in modulating energy, water and carbon fluxes is critical to quantifying the variability in energy, carbon, and water balances across landscapes. Rangeland ecosystems are often a patchy mosaic of vegetation types, making measurement and modeling of surface energy fluxes in these environments particularly challenging. Surface energy fluxes measured at three rangeland sites were evaluated, and the data were used to improve simulations of a plant canopy energy balance model, the Simultaneous Heat and Water (SHAW) model. Good agreement between measured and modeled energy fluxes suggest that they can be measured and simulated reliably in these complex environments, but care must be used in the interpretation of the results. Scientists can capitalize upon these results to better describe and model these ecosystems and their response to climate change.
Technical Abstract: Rangeland ecosystems are often characterized by a patchy mosaic of vegetation types, making measurement and modeling of surface energy fluxes particularly challenging. The purpose of this study was to evaluate surface energy fluxes measured using eddy correlation at three rangeland sites, and use the data to improve simulations of turbulent energy fluxes in a multi-layer plant canopy model, the Simultaneous Heat and Water (SHAW) model. Model modifications included adjustment of the wind profile roughness parameters for sparse canopies, and introducing Lagrangian far field turbulent transfer equations (L-theory) in lieu of the K-theory approach used previously. There was relatively little difference in simulated energy fluxes for the aspen canopy using L-theory versus K-theory turbulent transfer equations, but L-theory tracked canopy air temperature profiles better. Upward sensible heat flux was observed above aspen trees, within the aspen understory, and above sagebrush throughout the active snowmelt season. Model simulations confirmed the observed upward sensible flux during snowmelt was due to solar heating of the aspen limbs and sagebrush. Thus, the three EC systems were unable to properly quantify fluxes at the snow surface when vegetation was present, illustrating the difficulty in using EC systems to quantify energy fluxes at the snow surface with vegetation present. Good agreement between measured and modeled energy fluxes suggest that they can be measured and simulated reliably in these complex environments, but care must be used in the interpretation of the results.